98c co2 leak

lately my tippmann's been leaking a lot of co2 and i'm not sure how exactly to fix it. i have a 20oz tank and it only lasted about 250 rounds with a clearly heard hissing of the co2 from the gun. i just refilled the tank today and upon screwing in the co2 tank i clearly saw the gas leaking out from the top of the macroline, in front of the bolt which was cocked back, and i think also the velocity screw. i've tried tefloning the macroline's in the past and have opened the gun and cleaned it all, including the valve. i don't know what the problem is and can't play til i fix this because i've already used up a quarter of my tank just firing 20 rounds. any advice is appreciated